The correct answer is A) temperature rise. The nameplates of shipboard AC motors display the operational information data required by applicable standards and regulations, such as the temperature rise of the motor. This is an important specification as it indicates the maximum allowable temperature of the motor during operation, which is crucial for ensuring safe and reliable performance. The other options, such as type of overload protection, locked-rotor torque, and rated slip, while also important motor specifications, are not typically included on the nameplate as the primary operational data. The temperature rise is the key information that needs to be clearly displayed on the nameplate.